Changes in cutaneous innervation in patients with chronic pain after burns

Background: Chronic pain is a common occurrence for burn patients and has significant impact on quality of life. However, the etiology is not well understood. Understanding the mechanisms underlying the restoration of sensory function and the development of chronic pain after burn is critical to improving long-term outcomes. Objective: To determine whether cutaneous innervation in burn patients with chronic pain is altered when compared to patients without chronic pain. Methods: Twelve patients with unilateral injury and who reported chronic pain were recruited. Each patient underwent sensory function testing and both scar and matched site uninjured skin biopsy. Biopsies were analyzed for total nerve density and nociceptive C-fiber density using immunohistochemistry. Results were compared to a control group of 33 patients with unilateral injury and no reported long-term pain. Results: Sensory function was significantly diminished in scar compared to uninjured tissue in both study groups, but chronic pain patients did not have significantly diminished function when compared to control. Total nerve density was not significantly different between scar and uninjured sites in either group, or between groups. However, the density of nociceptive nerve fibers was significantly elevated in both uninjured (p = 0.0193) and scar sites (p = 0.0316) of the patients with chronic pain when compared to the control group. Conclusions: This data suggests that differences in cutaneous innervation may contribute to chronic pain after burn. There also appears to be a systemic difference in cutaneous innervation extending to distal uninjured sites. Therefore efforts to affect cutaneous reinnervation after burn may lead to less patients experiencing chronic pain